The invention relates to a sensor for a receiving device for cooperation with an optical fiber for converting a beam form signal outputted by the optical fiber into an electric signal, the sensor comprising two or more mutually separated sensor elements.
The invention also relates to a receiving device for cooperation with an optical fiber, comprising said sensor for converting a signal in the form of a modulated beam exiting the optical fiber into an electric signal.
Such a sensor is known from a Japanese patent application JP-A-111351818 laid open to public inspection. Said document discloses a two-dimensional sensor in which the sensor elements are temperature sensors which undergo a temperature change upon being hit by the beam exiting the optical fiber, which temperature change can be detected by the processing electronics that are provided. Each sensor element comprises a first and a second temperature sensor. The sensor elements are arranged in rows and columns. All the first temperature sensors of a row are interconnected, and all the second temperature sensors of a column are interconnected. The interconnected temperature sensors are coupled to a voltage detector. By detection which row and which column deliver the signal different from that delivered by the other rows and columns it can be determined at what sensor position the beam hit the sensor.
Such a sensor is not suitable at all for converting information present in the beam into a different type of signal.
Fiber-optical communication systems are capable of supporting signals having relatively high widths, and high bit rates, respectively, for example 2.5 GHs to 4 GHs for SONET applications. In existing fiber-optical communication systems, the electrical components are bit-serial: a single laser diode or LED for generating the optical signal transmitted through the optical fiber, a single PIN diode for detecting the beam exiting the optical fiber and multiple high-speed bipolar or GaAs circuits for processing the signals which control the laser diode or LED or which originate from the PIN photo diode. Such electrical components are costly and the described signal chain cannot be further integrated by using the process technology by means of which they are manufactured.
In existing fiber-optical receiver chains it is known to implement said further processing electronics in a multipath structure, in which parallel processing of signals can take place, after the beam has been detected by means of the PIN photo diode and has been coupled to said further processing electronics via an initial bipolar or GaAs detector chip.
In spite of the parallel processing in the further path, the known receiver chains are still limited by the fact that only one PIN photo diode is present for detecting the single beam outputted by the optical fiber and converting it into an electric signal. High speed operating devices suitable for working with the above-mentioned signals are expensive.
It is therefore an object of the invention to provide a sensor being capable of handling said signals using cheaper technology.
According to the invention, this object is achieved in that an output of each sensor element is coupled to an input of an amplifying element, an output of each amplifying element is coupled to an input of an analog to digital converter associated with the amplifying element, and in that the sensor elements and the amplifying elements coupled thereto are provided on a single semiconductor chip.
As a result, the same eceiving area, subdivided in multiple small sensor elements, is obtained for sensors for which so far one large PIN photodiode was required in order to generate a sufficiently strong signal, with the inherent drawback that the large capacitance resulted in a poor performance at high frequencies. Each of said smaller sensor elements has its own amplifying element and only a small capacitance is present for each sensor element, so that a satisfactory performance is possible at high frequencies as well, while the size of the total sensitive surface area does not differ from the size of the sensitive surface area of the known PIN photodiode.
In an embodiment of a sensor according to the invention the analog to digital converters are arranged on the semiconductor chip.
As a result, the signal detection from the beam exiting the fiber including the digitization of the electric signals is realized at a relatively high rate, at high frequencies, on a single chip, and in parallel.
In another embodiment of a sensor according to the invention the sensor elements are arranged within a predetermined area on the semiconductor chip, and the spatial density of sensor elements in said predetermined area is substantially constant.
As a result, the output signals from the various sensor elements exhibit a high degree of uniformity.
Another result is that less stringent requirements are imposed on the optical treatment of the beam outputted by the optical fiber.
In an embodiment a receiver device designed for cooperation with an optical fiber and comprising a sensor for converting a signal in the form of a modulated beam outputted by the optical fiber is presented. The device comprises the sensor as described above, the circuits on the semiconductor chip are clock-controlled, a clock rate for the circuits is lower than a clock rate corresponding to the bit transfer rate of the modulated beam, means for reconstructing the signals in the beam from signals delivered by the sensor elements at the clock rate for the circuits are present.
As a result, the frequency requirements imposed on the technology for the circuits on the single semiconductor chip of the sensor are less stringent than the requirements imposed to each individual sensor element for detecting the modulation in the exiting modulated beam.
In another embodiment of the sensor elements are organized in groups, the reconstruction means comprising control means which are arranged for reading the sensor elements in groups, and the number of groups being substantially equal to the ratio between the clock rate corresponding to the bit transfer rate of the modulated beam and the clock rate for the integrated circuits.
As a result, it is possible to detect signals that are present in the outputting beam at a frequency which is much higher than a first maximum frequency, using a technology that is suitable for said first maximum frequency.